Thursday, May 12, 2011

Hot off the presses! May 13 CEL

The May 13 issue of the CEL is now up on Pubget (About CEL): if you're at a subscribing institution, just click the link in the latest link at the home page. (Note you'll only be able to get all the PDFs in the issue if your institution subscribes to Pubget.)

Latest Articles Include:

  • In This Issue
    - CEL 145(4):485, 487 (2011)
  • Learning and Memory
    - CEL 145(4):489, 491 (2011)
    How do we learn and remember? How do our brains change with experience? Why do we forget? This issue's Select features recent articles that address these questions. Four studies provide new perspectives on how molecular changes at individual synapses influence behaviors, supply insight into diseases typified by learning and memory deficits, and highlight how spatial information is integrated to build cognitive maps.
  • Jürg Tschopp 1951–2011
    - CEL 145(4):493-494 (2011)
  • Estrogen Receptor Transrepresses Brain Inflammation
    - CEL 145(4):495-497 (2011)
    Estrogen receptors (ERs) have long been implicated in the etiology of multiple sclerosis, but no clear molecular mechanisms have linked ERs to the disease's pathology. Now Saijo et al. (2011) provide evidence that ERβ activates a transrepression pathway that suppresses inflammation and inhibits progression of pathology in a mouse model of multiple sclerosis.
  • Metabolic Homeostasis: HDACs Take Center Stage
    - CEL 145(4):497-499 (2011)
    Hormonal regulation of glucose and lipid metabolism is pivotal for metabolic homeostasis and energy balance. Two studies in this issue of Cell (Mihaylova et al., 2011 and Wang et al., 2011) introduce a new conserved signaling mechanism controlling catabolic gene expression: class IIa histone deacetylases (HDACs) regulate Foxo activity in Drosophila and mice.
  • A Hormone Sends Instant Messages to the Genome
    - CEL 145(4):499-501 (2011)
    Bridging a gap between transcriptomics and the study of cis-acting elements (cistromics), Hah et al. (2011) apply a next-generation sequencing technique to gain an unprecedented view of the changes in RNA synthesis that occur following estrogen receptor activation in human breast cancer cells.
  • Paused RNA Polymerase II as a Developmental Checkpoint
    - CEL 145(4):502-511 (2011)
    The textbook view of gene activation is that the rate-limiting step is the interaction of RNA polymerase II (Pol II) with the gene's promoter. However, studies in a variety of systems, including human embryonic stem cells and the early Drosophila embryo, have begun to challenge this view. There is increasing evidence that differential gene expression often depends on the regulation of transcription elongation via the release of Pol II from the proximal promoter. I review the implications of this mechanism of gene activation with respect to the orderly unfolding of complex gene networks governing animal development.
  • Mapping the NPHP-JBTS-MKS Protein Network Reveals Ciliopathy Disease Genes and Pathways
    - CEL 145(4):513-528 (2011)
    Nephronophthisis (NPHP), Joubert (JBTS), and Meckel-Gruber (MKS) syndromes are autosomal-recessive ciliopathies presenting with cystic kidneys, retinal degeneration, and cerebellar/neural tube malformation. Whether defects in kidney, retinal, or neural disease primarily involve ciliary, Hedgehog, or cell polarity pathways remains unclear. Using high-confidence proteomics, we identified 850 interactors copurifying with nine NPHP/JBTS/MKS proteins and discovered three connected modules: "NPHP1-4-8" functioning at the apical surface, "NPHP5-6" at centrosomes, and "MKS" linked to Hedgehog signaling. Assays for ciliogenesis and epithelial morphogenesis in 3D renal cultures link renal cystic disease to apical organization defects, whereas ciliary and Hedgehog pathway defects lead to retinal or neural deficits. Using 38 interactors as candidates, linkage and sequencing analysis of 250 patients identified ATXN10 and TCTN2 as new NPHP-JBTS genes, and our Tctn2 mouse! knockout shows neural tube and Hedgehog signaling defects. Our study further illustrates the power of linking proteomic networks and human genetics to uncover critical disease pathways.
  • Double-Strand Break Repair-Independent Role for BRCA2 in Blocking Stalled Replication Fork Degradation by MRE11
    - CEL 145(4):529-542 (2011)
    Breast cancer suppressor BRCA2 is critical for maintenance of genomic integrity and resistance to agents that damage DNA or collapse replication forks, presumably through homology-directed repair of double-strand breaks (HDR). Using single-molecule DNA fiber analysis, we show here that nascent replication tracts created before fork stalling with hydroxyurea are degraded in the absence of BRCA2 but are stable in wild-type cells. BRCA2 mutational analysis reveals that a conserved C-terminal site involved in stabilizing RAD51 filaments, but not in loading RAD51 onto DNA, is essential for this fork protection but dispensable for HDR. RAD51 filament disruption in wild-type cells phenocopies BRCA2 deficiency. BRCA2 prevents chromosomal aberrations on replication stalling, which are alleviated by inhibition of MRE11, the nuclease responsible for this form of fork instability. Thus, BRCA2 prevents rather than repairs nucleolytic lesions at stalled replication forks to maintain! genomic integrity and hence likely suppresses tumorigenesis through this replication-specific function.
  • Establishment and Maintenance of Alternative Chromatin States at a Multicopy Gene Locus
    - CEL 145(4):543-554 (2011)
    In eukaryotes, each of the more than 100 copies of ribosomal RNA (rRNA) genes exists in either an RNA polymerase I transcribed open chromatin state or a nucleosomal, closed chromatin state. Open rRNA genes guarantee the cell's supply with structural components of the ribosome, whereas closed rRNA genes ensure genomic integrity. We report that the observed balance between open and closed rRNA gene chromatin states in proliferating yeast cells is due to a dynamic equilibrium of transcription-dependent removal and replication-dependent assembly of nucleosomes. Pol I transcription is required for the association of the HMG box protein Hmo1 with open rRNA genes, counteracting replication-independent nucleosome deposition and maintaining the open rRNA gene chromatin state outside of S phase. The findings indicate that the opposing effects of replication and transcription lead to a de novo establishment of chromatin states for rRNA genes during each cell cycle.
  • An Epigenetic Signature for Monoallelic Olfactory Receptor Expression
    - CEL 145(4):555-570 (2011)
    Constitutive heterochromatin is traditionally viewed as the static form of heterochromatin that silences pericentromeric and telomeric repeats in a cell cycle- and differentiation-independent manner. Here, we show that, in the mouse olfactory epithelium, olfactory receptor (OR) genes are marked in a highly dynamic fashion with the molecular hallmarks of constitutive heterochromatin, H3K9me3 and H4K20me3. The cell type and developmentally dependent deposition of these marks along the OR clusters are, most likely, reversed during the process of OR choice to allow for monogenic and monoallelic OR expression. In contrast to the current view of OR choice, our data suggest that OR silencing takes place before OR expression, indicating that it is not the product of an OR-elicited feedback signal. Our findings suggest that chromatin-mediated silencing lays a molecular foundation upon which singular and stochastic selection for gene expression can be applied.
  • Distinct p53 Transcriptional Programs Dictate Acute DNA-Damage Responses and Tumor Suppression
    - CEL 145(4):571-583 (2011)
    The molecular basis for p53-mediated tumor suppression remains unclear. Here, to elucidate mechanisms of p53 tumor suppression, we use knockin mice expressing an allelic series of p53 transcriptional activation mutants. Microarray analysis reveals that one mutant, p5325,26, is severely compromised for transactivation of most p53 target genes, and, moreover, p5325,26 cannot induce G1-arrest or apoptosis in response to acute DNA damage. Surprisingly, p5325,26 retains robust activity in senescence and tumor suppression, indicating that efficient transactivation of the majority of known p53 targets is dispensable for these pathways. In contrast, the transactivation-dead p5325,26,53,54 mutant cannot induce senescence or inhibit tumorigenesis, like p53 nullizygosity. Thus, p53 transactivation is essential for tumor suppression but, intriguingly, in association with a small set of novel p53 target genes. Together, our studies distinguish the p53 transcriptional programs invol! ved in acute DNA-damage responses and tumor suppression—a critical goal for designing therapeutics that block p53-dependent side effects of chemotherapy without compromising p53 tumor suppression.
  • An ADIOL-ERβ-CtBP Transrepression Pathway Negatively Regulates Microglia-Mediated Inflammation
    - CEL 145(4):584-595 (2011)
    Microglia and astrocytes play essential roles in the maintenance of homeostasis within the central nervous system, but mechanisms that control the magnitude and duration of responses to infection and injury remain poorly understood. Here, we provide evidence that 5-androsten-3β,17β-diol (ADIOL) functions as a selective modulator of estrogen receptor (ER)β to suppress inflammatory responses of microglia and astrocytes. ADIOL and a subset of synthetic ERβ-specific ligands, but not 17β-estradiol, mediate recruitment of CtBP corepressor complexes to AP-1-dependent promoters, thereby repressing genes that amplify inflammatory responses and activate Th17 T cells. Reduction of ADIOL or ERβ expression results in exaggerated inflammatory responses to TLR4 agonists. Conversely, the administration of ADIOL or synthetic ERβ-specific ligands that promote CtBP recruitment prevents experimental autoimmune encephalomyelitis in an ERβ-dependent manner. These findings provide ev! idence for an ADIOL/ERβ/CtBP-transrepression pathway that regulates inflammatory responses in microglia and can be targeted by selective ERβ modulators. PaperClip To listen to this audio, enable JavaScript on your browser. However, you can download and play the audio by clicking on the icon below Download this Audio (5759 K)
  • A Hormone-Dependent Module Regulating Energy Balance
    - CEL 145(4):596-606 (2011)
    Under fasting conditions, metazoans maintain energy balance by shifting from glucose to fat burning. In the fasted state, SIRT1 promotes catabolic gene expression by deacetylating the forkhead factor FOXO in response to stress and nutrient deprivation. The mechanisms by which hormonal signals regulate FOXO deacetylation remain unclear, however. We identified a hormone-dependent module, consisting of the Ser/Thr kinase SIK3 and the class IIa deacetylase HDAC4, which regulates FOXO activity in Drosophila. During feeding, HDAC4 is phosphorylated and sequestered in the cytoplasm by SIK3, whose activity is upregulated in response to insulin. SIK3 is inactivated during fasting, leading to the dephosphorylation and nuclear translocation of HDAC4 and to FOXO deacetylation. SIK3 mutant flies are starvation sensitive, reflecting FOXO-dependent increases in lipolysis that deplete triglyceride stores; reducing HDAC4 expression restored lipid accumulation. Our results reveal a horm! one-regulated pathway that functions in parallel with the nutrient-sensing SIRT1 pathway to maintain energy balance.
  • Class IIa Histone Deacetylases Are Hormone-Activated Regulators of FOXO and Mammalian Glucose Homeostasis
    - CEL 145(4):607-621 (2011)
    Class IIa histone deacetylases (HDACs) are signal-dependent modulators of transcription with established roles in muscle differentiation and neuronal survival. We show here that in liver, class IIa HDACs (HDAC4, 5, and 7) are phosphorylated and excluded from the nucleus by AMPK family kinases. In response to the fasting hormone glucagon, class IIa HDACs are rapidly dephosphorylated and translocated to the nucleus where they associate with the promoters of gluconeogenic enzymes such as G6Pase. In turn, HDAC4/5 recruit HDAC3, which results in the acute transcriptional induction of these genes via deacetylation and activation of FOXO family transcription factors. Loss of class IIa HDACs in murine liver results in inhibition of FOXO target genes and lowers blood glucose, resulting in increased glycogen storage. Finally, suppression of class IIa HDACs in mouse models of type 2 diabetes ameliorates hyperglycemia, suggesting that inhibitors of class I/II HDACs may be potentia! l therapeutics for metabolic syndrome.
  • A Rapid, Extensive, and Transient Transcriptional Response to Estrogen Signaling in Breast Cancer Cells
    - CEL 145(4):622-634 (2011)
    We report the immediate effects of estrogen signaling on the transcriptome of breast cancer cells using global run-on and sequencing (GRO-seq). The data were analyzed using a new bioinformatic approach that allowed us to identify transcripts directly from the GRO-seq data. We found that estrogen signaling directly regulates a strikingly large fraction of the transcriptome in a rapid, robust, and unexpectedly transient manner. In addition to protein-coding genes, estrogen regulates the distribution and activity of all three RNA polymerases and virtually every class of noncoding RNA that has been described to date. We also identified a large number of previously undetected estrogen-regulated intergenic transcripts, many of which are found proximal to estrogen receptor binding sites. Collectively, our results provide the most comprehensive measurement of the primary and immediate estrogen effects to date and a resource for understanding rapid signal-dependent transcriptio! n in other systems.
  • NEMO/NLK Phosphorylates PERIOD to Initiate a Time-Delay Phosphorylation Circuit that Sets Circadian Clock Speed
    - CEL 145(4):635 (2011)
  • SnapShot: BMP Signaling in Development
    - CEL 145(4):636-636.e2 (2011)

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